Abstract In Vitro Diagnostic Solutions (IVDS) proposes to develop the only point-of-care (POC) test for the determination of L-phenylalanine (Phe) from a finger or heel-stick sample. The point-of-care test, the ?PKU Now? will be used as a home monitoring device for PKU patients and for diagnostic testing in developing regions. The PKU Now will provide immediate feedback of whole blood phe concentration, allowing for stricter dietary compliance, improve the quality of life, and reduce healthcare costs. In Phase I studies, we will resolve three outstanding issues before commercializing the system, namely eliminating interferences (Aim-1), eliminating hematocrit bias in the range of 32% to 60% (Aim-2), and establishing agreement between the ?PKU Now? and a laboratory reference method (Aim-3). Phenylketonuria (commonly known as PKU) is an inherited disorder that increases the levels of a substance called phenylalanine in the blood. PKU is the most common disorder of amino acid metabolism, effecting 1 in 8,000 people, globally. Most cases of PKU are detected shortly after birth by newborn screening. Individuals affected by PKU must monitor and control phe levels throughout their lives to avoid neurological complications including; permanent intellectual disabilities, seizures, delayed development, behavioral problems, and psychiatric disorders. Whole blood is collected in EDTA tubes or spotted onto Dried Blood Spot (DBS) Cards by parents, patients or caregivers. These samples are sent to laboratories for measurement by tandem mass spec and results can take days to weeks. This complicated process for monitoring and controlling phe levels, results in non-compliance, a decrease in quality of life, as well as increased healthcare costs for treating complications. The PKU Now will provide real time phe levels, allowing parents and caregivers to promptly adjust their diets to help maintain optimal phenylalanine levels. In Vitro Diagnostic Systems (IVDS) has developed a prototype POC test, in which phe can be quantified from a 20 microliters of sample. Upon successful validation of ?PKU Now?, Phase II will ensure linearity and precision, establish intra-day and inter-day precision, and evaluate preclinical data against tandem mass spec analysis, all following CLSI guidelines. ?PKU Now? will be the only point-of-care testing device (POCT) that will allow the accurate measurement of L-phenylalanine (phe) levels from a finger or heel-stick.